In What Layer Of The Earth's Atmosphere Do Artificial Satellites Orbit The Earth?

You can consider most satellites to be in space, but in terms of the Earth's atmosphere, they occupy regions called the thermosphere and the exosphere. The layer through which a satellite orbits depends on the satellite's function and the kind of orbit it has. Since the launch of Sputnik in the 1950s, spacefaring countries have put thousands of satellites into orbit around the Earth and even other planets. They serve many different purposes, from complex space stations like the International Space Station to the Global Positioning System that helps you find your way home.

The thermosphere is a region of very high temperature that extends from the top of the mesosphere at around 85 kilometers (53 miles) up to 640 kilometers (400 miles) above the Earth's surface. It is called the thermosphere because temperatures can reach up to 1,500 degrees Celsius (2,732 degrees Fahrenheit). However, despite the high temperatures, the pressure is very low, so satellites don't suffer heat damage.

Above the thermosphere sits a final layer called the exosphere, which extends up to 10,000 kilometers (6,200 miles) above the Earth, depending on how it is defined. Some definitions of the exosphere include all space up until the point where atoms get knocked away by solar wind. No distinct upper boundary exists since the exosphere has no pressure and molecules float freely here. Eventually, the exosphere gives way to space outside of the Earth's influence.

The lowest-orbiting satellites occupy Low Earth Orbit, or LEO, which includes any orbit below 2,000 kilometers (1,243 miles). Satellites at this altitude circle the Earth very quickly and their orbits degrade faster, which means they eventually fall back to Earth if not kept up by thrusters. The International Space Station is in LEO and most satellites in LEO fly through the thermosphere, though those at the upper limit of LEO reach into the exosphere. Scientific research satellites are typically put into LEO so they can more closely monitor activities on Earth.

Satellites above LEO all orbit through the exosphere and can maintain their orbits for decades without adjustment. Weather and communication satellites occupy higher orbits because they need longer views of a given area of the planet to either carry transmissions or record data. At the top of High Earth Orbit is geosynchronous orbit. Any satellite here will have an orbital period the same as the Earth's. A special type of geosynchronous orbit is the geostationary orbit, which runs along the equator. This keeps the satellite at the same point in the sky throughout the entire orbit.